Process for the recovery of steam emitted in a liquid distribution plant

ABSTRACT

A method of recovering vapor emitted in a liquid dispensing installation comprising: liquid dispensing means (P L ) adapted to cause said liquid to flow with a liquid flowrate Q L  ; vapor recovery means (P V ) adapted to cause said vapor to flow with a vapor flowrate Q V  along a pipe (120), said vapor flowrate Q V  being controlled by a parameter G. According to the invention, the method includes the following steps: establishing an equation G=F (Q V , {p i  }) relating the parameter G to the vapor flowrate Q V  and to parameters p i  characteristic of the recovery means and said pipe (120); determining an initial value {p i  } o  of the parameters p i  ; on each dispensing k of liquid: measuring the liquid flowrate Q Lk  and determining a value G k  of the parameter G from the equation: 
     
         G.sub.k =F (Q.sub.Lk, {p.sub.i }.sub.k-1); 
    
     determining a new value {p i  } k  of the parameters p i  to be used for the next dispensing k+1 of liquid. Application to dispensing fuel for motor vehicles.

FIELD OF THE INVENTION

The present invention concerns a method of recovering vapor emitted byan installation for dispensing a liquid while said liquid is beingdispensed into a tank.

The invention finds a particularly advantageous application in the fieldof dispensing fuel for motor vehicles, for example, for recovering thehydrocarbon vapor that escapes from the tank of the vehicle while it isbeing filled with liquid fuel.

BACKGROUND OF THE INVENTION

An installation for dispensing liquid such as fuel for motor vehiclesgenerally comprises means for dispensing said liquid essentiallycomprising volumeters fitted with pumps adapted to cause the fuel toflow with a liquid flowrate Q_(L) between a storage tank and the fueltank of the vehicles. The volumeters also include a liquid measuringdevice connected to a pulse generator enabling a computer to establishthe volume and the price of the fuel delivered, which are shown in theclear on a display with which the volumeters are equipped.

If the hydrocarbon vapor emitted is to be recovered, said installationincludes recovery means adapted to cause said vapor to circulate with avapor flowrate Q_(V) along a pipe between the vehicle fuel tank and arecovery tank, for example the storage tank, the vapor flowrate Q_(V)being controlled by a parameter G characteristic of said recovery meansso as to maintain between the vapor flowrate Q_(V) and the liquidflowrate Q_(L) a relation of proportionality Q_(V) =kQ_(L) with k equalto or close to 1.

Said recovery means usually comprise a pump aspirating the vapor fromthe fuel tank in order to return it to the hydrocarbon storage tank. Thecharacteristic parameter G is the rotation speed w of said pump which iscontrolled by the pulse generator of the dispensing means.

However, in most cases there is no simple way to impose a pump speed wproportional to the liquid flowrate Q_(L).

Operating conditions can differ greatly from one installation toanother, in terms of:

head losses in the recovery pipe upstream and downstream of the pump,

the possible presence of calibrated valves at the recovery tank whichcan generate within the latter a pressure different from atmosphericpressure and corresponding to an additional hydraulic resistance on therecovery pipe,

internal leakage of the recovery pump, dependent on theupstream-downstream pressure difference, which affects its efficiency.

To summarize, to obtain a given vapor flowrate Q_(V), it is necessary toimpose on the recovery pump a rotation speed w that depends on theinstallation.

To allow for the parameters mentioned above it is standard practice tocalibrate the complete installation when installed on the site. Duringthis calibration a recovery pump speed w is fixed and the correspondingvapor flowrate Q_(V) is measured using a flowmeter or a gas meter. Atable (w, Q_(V)) is drawn up in this way relating the speed w and thevapor flowrate Q_(V) with a sufficient number of points to define thecharacteristic of the pump under these operating conditions. This tableis stored in memory in a microprocessor.

In normal operation, the flowmeter is removed and, during dispensing ofhydrocarbons at a liquid flowrate Q_(L), the microprocessor looks up inthe table the speed w to be imposed on the recovery pump such that Q_(V)=Q_(L).

This prior art recovery method has the following disadvantages, however:

head losses in the recovery pipe can vary with time because of:

progressive partial blocking with dust,

a change in the cross-section of the elastomer hoses due to theprolonged presence of hydrocarbons. This applies in particular to thepart of the pipe upstream of the pump, which generally comprises anelastomer tube surrounded with pressurized liquid, this partrepresenting the core of a coaxial hose.

the internal leakage of the pump can vary because of wear, as in vanepumps, for example.

the density of the vapor varies with the nature of the hydrocarbons andthe temperature of the vehicle fuel tanks, which modifies the effect ofthe upstream and downstream head losses.

the vapor pressure in the recovery tank can also vary with the nature ofthe hydrocarbons and the temperature.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is that ofproposing a method of recovering vapor emitted in a liquid dispensinginstallation when dispensing said liquid into a tank, said installationcomprising:

liquid dispensing means adapted to cause said liquid to flow with aliquid flowrate Q_(L) between a storage tank and said tank,

vapor recovery means adapted to cause said vapor to flow with a vaporflowrate Q_(V) along a pipe between said tank and a recovery tank, saidvapor flowrate Q_(V) being controlled by a parameter G characteristic ofsaid recovery means,

which method, given the slow evolution of the parameters characteristicof the flow of vapor along the recovery pipe, would enable deferredrecalibration of the characteristic parameter G as a function of thevapor flowrate Q_(v).

In accordance with the present invention, the solution to this technicalproblem resides in the fact that said method includes the followingsteps:

establishing an equation

    G=F(Q.sub.v, {P.sub.i })

relating the parameter G to the vapor flowrate Q_(V) and to parametersp_(i) characteristic of the recovery means and said pipe,

determining an initial value {P_(i) }_(o) of the parameters P_(i),

on each dispensing k of liquid:

measuring the liquid flowrate Q_(Lk) and determining a value G_(k) ofthe parameter G to be imposed on the recovery means by the equation:

    G.sub.k =F(Q.sub.Lk, {P.sub.i }.sub.k-1)

determining a new value {P_(i) }_(k) of the parameters P_(i) to be usedfor the next dispensing k+1 of liquid.

Accordingly, during dispensing of liquid, a value determined fromparameters calculated during the preceding dispensing is used for thecharacteristic parameter G and at least one measurement is effected inorder to calculate new values for said parameters that will be used forthe next dispensing.

As will be seen in detail below, two particular, but not exclusive,embodiments of the method of the invention are proposed.

In a first embodiment, the recovery means comprising a pump, saidparameter G is the rotation speed w of said pump.

In a second embodiment, the recovery means comprising a pump and asolenoid valve, said parameter G is the hydraulic resistance imposed bysaid solenoid valve, the rotation speed w of the pump being constant. Toa first approximation, the various parameters p_(i) characteristic ofthe recovery means and of the pipe are considered to be independent ofthe vapor flowrate Q_(v). Nevertheless, some of these parameters mayvary with said vapor flowrate. This applies in particular to theinternal leakage coefficient a of vane pumps if the vanes are notprecisely guided. The method of the invention must therefore be adaptedto suit this particular situation. This is why, in accordance with theinvention, there is provision for one parameter p of the parametersp_(i) to vary with the vapor flowrate Q_(V) :

an initial table [p_(o) ^(j), Q_(V) ^(j) ] (j=1, . . . , N) isestablished linking N values of the parameter p to N values of the vaporflowrate Q_(V),

on each dispensing k of liquid:

a value p^(j) _(k-1) of the parameter p is used in the equation

    G.sub.k =F(Q.sub.Lk, {p.sub.i }.sub.k-1)

such that [p^(j) ]_(k-1), Q^(j) _(V) =Q_(Lk) ]

the vapor flowrate Q_(Vk) is measured and a corresponding value p_(k) ofthe parameter p is determined,

a coefficient A_(k) is calculated such that

    A.sub.k =p.sub.k /p.sup.j'.sub.o with [p.sup.j'.sub.o, Q.sup.j'.sub.V =Q.sub.Vk ]

a new table

[p^(j) _(k), Q^(j) _(V) ] is established for all values of j with p^(j)_(k) =A_(k) p^(j) _(o).

BRIEF DESCRIPTION OF THE DRAWINGS

The following description with reference to the accompanying drawings,given by way of non-limiting example, shows in what the inventionconsists and how it can be put into practice.

FIG. 1 is a general schematic of a liquid dispensing installation usinga vapor recovery method of the invention.

FIG. 2 is a schematic of the vapor recovery circuit from FIG. 1 in thecase where the recovery pump has no internal leaks.

FIG. 3 is a schematic of the vapor recovery circuit from FIG. 1 in thecase where the recovery pump has an internal leak.

FIG. 4 is a schematic of the vapor recovery circuit from FIG. 1 usingtwo pressure regulators.

FIG. 5 is a schematic of a vapor recovery circuit with two recoverychannels feeding a common pipe.

FIG. 6 is a schematic of the vapor recovery circuit from FIG. 1 with aregulator solenoid valve downstream of the recovery pump.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The FIG. 1 schematic shows an installation for dispensing liquid, forexample fuel, into the fuel tank of a vehicle, not shown.

The installation comprises fuel dispensing means essentially consistingof a pump P_(L) adapted to cause said fuel L to flow with a liquidflowrate Q_(L) between a storage tank 100 and said fuel tank along apipe 110 to a dispensing nozzle 111.

As mentioned above, a volumeter 112, possibly incorporating the liquidpump P_(L), includes a measuring device 113 disposed on the pipe 110 inseries with the pump P_(L) so that a pulse generator 114 coupled to saidmeasuring device 113 supplies a pulse signal representative of theliquid flowrate Q_(L) that a computer 115 then converts into a volumeand a price sent to a display 116.

The FIG. 1 installation also comprises means for recovering the vapor Vemitted during the dispensing of the liquid into the fuel tank of thevehicle. In the FIG. 1 example, said recovery means primarily comprise apump P_(V) adapted to cause said vapor to flow at a vapor flowrate Q_(V)along a pipe 120 between the fuel tank, via the dispensing nozzle 111,and a recovery tank 100 which, in FIG. 1, is the liquid fuel storagetank.

Generally speaking, the recovery method of the invention consists inimposing on a parameter G characteristic of the recovery means, therotation speed w of the pump P_(V) in the FIG. 1 example, a value suchthat the resulting vapor flowrate Q_(V) is as close as possible to theliquid flowrate Q_(L).

To this end, there is established and stored in the memory of a circuit121 controlling the motor M_(V) of the pump P_(V) an equation

    G=F(Q.sub.V, {p.sub.i })

linking the parameter G to the vapor flowrate Q_(V) and to parametersp_(i) characteristic of the recovery means and of the recovery pipe 120,these parameters being explained hereinafter on an individual basis.

Then, after determining an initial value {p_(i) }_(o) of the parametersp_(i), on each dispensing k of liquid the liquid flowrate Q_(Lk) ismeasured using information supplied by the pulse generator 114 to thecontrol circuit 121 of the motor M_(V). The value G_(k) of the parameterG to be imposed on the recovery means is then determined by the equation

    G.sub.k =F(Q.sub.Lk, {p.sub.i }.sub.k-1)

in which {p_(i) }_(k-1) represents the value of the parameters p_(i)calculated during the previous dispensing k-1 of liquid.

During this dispensing k of liquid, a new value {p_(i) }_(k) of theparameters p_(i) to be used for the next dispensing k+1 of liquid isdetermined.

The recovery method of the invention is based on the idea of deferredupdating of the parameters governing the flow of vapor in the recoverypipe 120. Because the updating is done from one dispensing of liquid tothe next, the systematic error inherent in the method remains negligiblegiven the very slow drift with time of the parameters p_(i) that areessentially related to the vapor pump P_(V) and to the head losses inthe pipe 120.

FIG. 2 shows a first example of an application of the method of theinvention. In this example the recovery means comprise the vapor pumpP_(V) the rotation speed w of which constitutes the parameter Gcontrolling the vapor flowrate Q_(V).

Assuming that the pump P_(V) has no internal leakage (coefficient α=0),that the vapor is recovered at atmospheric pressure P_(A) and that therecovery tank 120 is also at atmospheric pressure P_(A) (zero pressurerise or pressure drop ΔPo), the equation linking the rotation speed w ofthe pump P_(V) and the vapor flowrate is written:

    w=Q.sub.V /V.sub.G (P'/P.sub.A)                            (1)

where V_(G) is the geometrical cyclic volume of the pump and P' is thepressure at the pump inlet. If R' is the hydraulic resistance in theupstream part of the recovery pipe 120:

    P.sub.A -P'=R'Q.sub.V.sup.n                                (2)

where n is equal to 7/4, but can be taken as equal to 2 for simplicity.

The equation (1) is then written:

    w=Q.sub.V /V.sub.G (1-R'Q.sub.V.sup.n /P.sub.A)

which represents the general formula G=F (Q_(V), {p_(i) }), theparameters p_(i) being the geometrical cyclic volume V_(G) and theupstream hydraulic resistance R'. The parameter V_(G) is constant andcan be measured once and for all at the factory. The initial value R'oof the parameter R' is determined by means of the equation (2) byimposing any rotation speed w on the pump P_(V) and measuring thepressure P' using a pressure sensor 122 and possibly a flowmeter, notshown, that supplies the corresponding vapor flowrate Q_(V). After thisinitialization phase the flowmeter is removed. The values of V_(G) andR'o are stored in a memory of the control circuit 121 of the motor M_(V)of the pump P_(V).

On the first dispensing of liquid said control circuit calculates thespeed w₁ to be imposed on the pump from the previously measured valuesV_(G), R'o and the liquid flowrate Q_(L1) received from the pulsegenerator 114 using the equation:

    W.sub.1 =Q.sub.L1 /V.sub.G (1-R'oQ.sup.n.sub.L1 /P.sub.A)

During this first dispensing, a measurement P'₁ of the pressure P' iseffected, for calculating the new value R'₁ of R' using two equations:

    Q.sub.v1 =w.sub.1 V.sub.G P'.sub.1 /P.sub.A

    R'.sub.1 =(P.sub.A -P'.sub.1)/Q.sup.n vl

R'₁ is used on the second dispensing, and so on.

The FIG. 3 schematic concerns a vapor pump P_(V) having an internal leak(non-zero value of coefficient α).

The general equation of the vapor recovery circuit is written:

    w=Q.sub.V /V.sub.G (P'/P.sub.A)+αΔP            (3)

ΔP being the pressure difference across the pump P_(V).

ΔP is related to the vapor flowrate Q_(V) by the equation:

    ΔP=(R'+R")Q.sup.n.sub.V =R Q.sup.n.sub.V

R" being the hydraulic resistance downstream of the recovery pipe 120.

Given that the following still applies

    P.sub.A -P'=R'Q.sup.n.sub.V

equation (3) is then written

    W=Q.sub.V /V.sub.G (1-R'Q.sub.V.sup.n /P.sub.A)+(αR)Q.sub.V.sup.n

The parameters p_(i) characteristic of the recovery circuit aretherefore V_(G), R' and αR. As previously, the geometric cyclic volumeV_(G) of the pump, which is constant, is measured in the factory. Theparameters R' and αR can be determined using an upstream pressure P'sensor 122 and a flowmeter 123 at the inlet of the pump P_(V) to measurethe vapor flowrate Q_(V). In reality, the flowrate Q_(1u) supplied bythe flowmeter 123 must be corrected for the pressure P':

    Q.sub.V =Q.sub.1u (P'/P.sub.A)

This is done automatically by the control circuit 121 of the motor M_(V)which receives P' and Q_(1u) in addition to the liquid flowrate Q_(L).

Given these conditions, the values of R' and αR are linked to Q_(V) andP' by the equations:

    R'=(P.sub.A -P')/Q.sup.n.sub.V

    (αR)=[w-Q.sub.V /V.sub.G (1-R'Q.sup.n.sub.V /P.sub.A)]/Q.sup.n.sub.V

The initial values R'o and (αR)o can be determined during a firstdispensing k=o during which the rotation speed w of the pump P_(V) ismeasured.

A pressure sensor P", not shown, can be placed at the outlet of the pumpP_(V) if the downstream hydraulic resistance R" has to be known, forexample to monitor the condition of the pipe 120 downstream of the pumpor to detect a problem. R" is deduced from:

    R"=(P.sub.A -P")/Q.sup.n.sub.V

The embodiment shown in the FIG. 4 schematic is designed to simplify theupdating of the parameters p_(i). To this end, the pressure P' sensor122, and possibly that giving the pressure P", is dispensed with andrespective pressure regulators 124 and 125 are disposed at the inlet andat the outlet of the pump P_(V). The regulator 124 is set to a set pointvalue corresponding to a pressure P' such that P_(A) -P' is constantregardless of the vapor flowrate Q_(V). Similarly, the regulator 125imposes a pressure P" such that P"-P_(A) is independent of Q_(V).

The conditions for correct operation of this system are:

    P.sub.A -P'>R'Q.sub.V.sup.n

    P"-P.sub.A >R"Q.sub.V.sup.n

Provided that the above conditions are satisfied, the general equation(3) is written:

    w=Q.sub.V P.sub.A /V.sub.G P'+α(P"-P')

or

    w=Q.sub.1u /V.sub.G +α(P"-P')

The only parameters p_(i) to be taken into consideration are V_(G) andα, R' and R" no longer being included in the equation of the recoverycircuit. V_(G) is determined in the factory and α can be calculated ateach dispensing from the equation:

    α=(w-Q.sub.V P.sub.A /V.sub.G P')/(P"-P')

or

    α=(w-Q.sub.1u /V.sub.G)/(P"-P')

The pressure inside the recovery tank 100 may not be equal toatmospheric pressure P_(A), with a positive or negative pressuredifference ΔPo due, for example, to the presence of a vent valve 130shown in FIG. 1.

In this case, the general equation (3) becomes:

    w=Q.sub.V P.sub.A /V.sub.G P'+αRQ.sup.n.sub.V +αΔPo

The last term αΔPo is a correction term equivalent to an initial speedw_(i). The latter can be determined during waiting periods between twodispensings as the minimal speed to be applied to the pump P_(V) toobtain a non-zero vapor flowrate Q_(V). The quantity w-w_(i) is thentreated as before with ΔPo=0.

FIG. 5 shows the schematic of an installation in which two vapor pumpsP_(Va), P_(Vb) feed a common small-bore pipe 12.

This is the case in fuel dispensing stations in particular where, tolimit the cost associated with the hydrocarbon vapor recoveryinstallation, a flexible tube is inserted in the suction pipe forreturning vapor to the recovery tank 100. This tube is generally commonto two pumps and has a common hydraulic resistance R_(c) that can behigh.

The two channels a and b of the FIG. 5 circuit being symmetrical, onlythe channel a is discussed.

The general equation concerning the flow of vapor in the channel a iswritten:

    w.sub.a =Q.sub.1ua /V.sub.Ga +α.sub.a ΔPa

with

    ΔPa=R.sub.a Q.sub.V.sup.n.sub.a +R.sub.c (Q.sub.Va +Q.sub.VG).sup.n

and

    R.sub.a =R'a+R"a

Taking the approximate value of 2 for n:

    w.sub.a =Q.sub.1ua /V.sub.Ga +α.sub.a (R.sub.a +R.sub.c)Q.sup.2.sub.Va +α.sub.a Rc(Q.sup.2.sub.Vb +2Q.sub.Va Q.sub.VG)

The last two terms correspond to a single channel of hydraulicresistance R_(a) +R_(c) and the third term is a correction term relatedto channel b.

If only channel a is delivering liquid, Q_(Vb) =0 and the third term isa null term. Of the first two terms, α_(a) (R_(a) +R_(c)) is stilldeduced by means of measurements of the flowrate Q_(1ua) (or Q_(Va)) andthe pressure P'a by means of the flowmeter 123a and the pressure sensor122a.

If both channels a and b deliver liquid simultaneously, the vaporflowrate and pressure measurements on channels a and b, associated withthe term α_(a) (R_(a) +R_(c)) calculated previously, enable α_(a) R_(c)to be deduced.

The FIG. 6 schematic shows a different embodiment of the vapor recoverymethod of the invention.

In this variant, the vapor is caused to flow in the recovery pipe 120 bya pump P_(V) with a fixed rotation speed w_(o) driven by a motor M_(V).

The vapor flowrate Q_(V) is regulated by a solenoid valve 126 downstreamof the pump P_(V) and having a variable hydraulic resistance Rx thevalue of which is imposed by a control circuit 121.

In this example, the parameter G characteristic of the recovery means isRx, related to the speed w_(o) of the pump P_(V) and to the vaporflowrate Q_(V) by the equation:

    Rx=(w.sub.o -Q.sub.V /V.sub.g (1-R'Q.sup.n V/P.sub.A)-(αR)Q.sup.n.sub.V)/αQ.sup.2 .sub.V

with,

    R=R'+R"

The parameters p_(i) to be determined are V_(G), R', R and α. Apart fromV_(G) , which is constant and measured in the factory, the other threeparameters can be calculated from the measurements from the flowmeter123 and from the pressure P' and P" supplied by the sensors 122 and 126:

    R'=(P.sub.A -P')/Q.sup.n

    R=R'+(P"-P.sub.A -R.sub.x Q.sup.2.sub.V)/Q.sup.n.sub.V

    α=(w.sub.o -Q.sub.V /V.sub.G (1-R'Q.sup.2).sub.V /P.sub.A)/(RQ.sup.n.sub.V +R.sub.a Q.sup.n.sub.V )

The solenoid valve 126 could equally well be disposed upstream of thevapor pump P_(V), of course, which would yield a system of equationsdifferent from but equivalent to those just derived.

Similarly, allowing for a recovery tank pressure different fromatmospheric pressure and for a return tube common to two pumps appliesin the same way to the embodiment just described using a solenoid valve.

The foregoing description does not allow for any variation with thevapor flowrate Q_(V) of the characteristic parameters governing the flowof vapor in the recovery pipe. For some types of pump the internalleakage coefficient a is known to depend on the vapor flowrate. In thiscase, an initial table is established by calibration on site, table[(αR)_(o) ^(j) Q'_(V) ^(j) ] for parameter αR, for example, relating Nvalues (j=1, . . . , N) of αR to N corresponding values of Q_(V) :

    ______________________________________                                        1            (αR).sub.o.sup.1                                                                     Qv.sup.1                                            .            .            .                                                   2            (αR).sub.o.sup.2                                                                     Qv.sup.2                                            .            .            .                                                   j            (αR).sub.o.sup.j                                                                     Qv.sup.j ← Q.sub.L1                            .            .            .                                                   j'           (αR).sub.o.sup.j'                                                                    Qv.sup.j'  ← Q.sub.V1                          .            .            .                                                   N            (αR).sub.o.sup.N                                                                     Qv.sup.N                                            ______________________________________                                    

On the first liquid dispensing k=1, the known liquid flowrate Q_(L1) canbe used to determine the value (αR)₁ ^(j), to be used in the generalflow equation, namely:

    [(αR).sub.1.sup.j, Q.sub.V.sup.j =Q.sub.L1 ]

During this same dispensing, the vapor flowrate Q_(V1) is measured andfrom it are deduced, on the one hand using the flow equations, a value(αR)₁ of the parameter αR and, on the other hand, using the initialtable, a value (αR)_(o) ^(j') :

    [(αR).sub.o.sup.j', Q.sub.V.sup.j' =Q.sub.V1 ]

The values Q_(L1) and V_(V1) may not correspond exactly to values Q_(V)^(j) from the table. Linear interpolation is then used.

A coefficient A₁ =(αR)₁ /(αR)^(j') _(o) is deduced for updating thewhole of the table that will be used for the next dispensing bymultiplying each value (αR)_(o) ^(j) by the coefficient A₁.

The new table is written:

    [(αR).sub.1.sup.j, Q.sub.v.sup.j with (αR).sub.1.sup.j =A.sub.1 (αR).sub.0.sup.j for any j.

The same procedure is followed for each dispensing, updating the tablerelative to the initial table stored in memory.

I claim:
 1. A method of recovering vapor emitted in a liquid dispensinginstallation during the dispensing of a liquid into a tank, saidinstallation comprising:liquid dispensing means adapted to cause saidliquid to flow with a liquid flowrate Q_(L) between a storage tank andsaid tank; vapor recovery means adapted to cause said vapor to flow witha vapor flowrate Q_(V) along a pipe between said tank and a recoverytank, said vapor flowrate Q_(V) being controlled by a parameter G (w ;R_(X)) characteristic of said recovery means; said method including thefollowing steps:establishing an equation

    G=F(Q.sub.V, {p.sub.i })

relating the parameter G to the vapor flowrate Q_(V) and to parametersp_(i) characteristic of the recovery means and said pipe; determining aninitial value {p_(i) }_(o) of the parameters p_(i) ; and on eachdispensing k of liquid:measuring the liquid flowrate Q_(LK) anddetermining a value G_(K) of the parameter G to be imposed on therecovery means from the equation

    G.sub.k =F (Q.sub.Lk, {p.sub.i }.sub.k-1),

and determining a new value {p_(i) }_(k) of the parameters p_(i) to beused for the next dispensing k+1 of liquid; wherein the recovery meanscomprises a pump, said parameter G is the rotation speed w of said pump,said pump having an internal leakage coefficient of value zero, saidequation

    w=F (Qv, {p.sub.i })

for a recovery tank at atmospheric pressure is given by:

    w=Qv/V.sub.G (1-R'Qv.sup.n /P.sub.A)

V_(G) being the geometrical cyclic volume of the pump, R' the hydraulicresistance of the pipe upstream of the pump, n a coefficient equal to7/4 and P_(A) atmospheric pressure, and in the said parameters p_(i)being the parameters V_(G) and R', the constant parameter V_(G) isdetermined by initial calibration of the pump, the value R'_(k) of theparameter R' on each dispensing k being determined from the measuredpressure P' at the inlet of the pump using the equations:

    Q.sub.VK =W.sub.k V.sub.G P'.sub.k /P.sub.A

    R'.sub.k =(P.sub.A -P'.sub.k)/Q.sup.n.sub.vk.


2. A method of recovering vapor emitted in a liquid dispensinginstallation during the dispensing of a liquid into a tank, saidinstallation comprising:liquid dispensing means adapted to cause saidliquid to flow with a liquid flowrate Q_(L) between a storage tank andsaid tank; vapor recovery means adapted to cause said vapor to flow witha vapor flowrate Q_(V) along a pipe between said tank and a recoverytank, said vapor flowrate Q_(V) being controlled by a parameter G (w ;R_(X)) characteristic of said recovery means; said method including thefollowing steps:establishing an equation

    G=F(Q.sub.V, {p.sub.i })

relating the parameter G to the vapor flowrate Q_(V) and to parametersp_(i) characteristic of the recovery means and said pipe; determining aninitial value {p_(i) }_(o) of the parameters p_(i) ; and on eachdispensing k of liquid:measuring the liquid flowrate Q_(LK) anddetermining a value G_(K) of the parameter G to be imposed on therecovery means from the equation

    G.sub.k =F (Q.sub.Lk, {p.sub.i }.sub.k-1)

determining a new value {p_(i) }_(k) of the parameters p_(i) to be usedfor the next dispensing k+1 of liquid; wherein the recovery meanscomprises a pump, said parameter G is the rotation speed w of said pump;said pump having an internal leakage coefficient α with a non-zerovalue, said equation

    w=F (Qv, {pi})

is given by:

    w=QV/V.sub.G (1-R'Qv.sup.n /P.sub.A)+(αR)Qv.sup.n

V_(G) being the geometrical cyclic volume of the pump, R' the hydraulicresistance of the pipe upstream of the pump, n a coefficient equal to7/4, P_(A) atmospheric pressure and R the total hydraulic resistance ofthe pipe, equal to the sum of the upstream hydraulic resistance R' andthe hydraulic resistance R" of the pipe downstream of the pump, andwherein said parameters P_(i) comprising V_(G), R' and αR, the constantparameter V_(G) is determined by initial calibration of the pump, thevalues R'_(k) and (αR)_(k) of the parameters R' and αR on eachdispensing k being determined from the measured vapor flowrate Qv andpressure P' at the inlet of said pump using the equations:

    R'.sub.k =(P.sub.A -P'.sub.k)/Q.sup.n.sub.Vk

    (αR).sub.k =[W.sub.k -Q.sub.vk /V.sub.G (1-R'.sub.k Q.sup.n.sub.Vk /P.sub.A)]/Q.sup.n.sub.Vk.


3. The method of claim 2, wherein the value R"_(k) of the hydraulicresistance R" downstream of the pump on each dispensing k is determinedfrom the measured pressure P" at the pump outlet using the equation

    R".sub.k =(P.sub.A -P".sub.k)/Q.sup.n.sub.Vk.


4. The method of claim 3, wherein said recovery tank has a pressuredifference Δp_(o) relative to atmospheric pressure, and there is addedto the calculated values of the speed w of the pump a quantity w_(i)equal to the minimal speed to be applied to the pump to obtain anon-zero vapor flowrate Q_(v), said quantity W_(o) being measuredbetween two dispensings of liquid.
 5. The method of claim 2, whereinsaid recovery tank has a pressure difference Δp_(o) relative toatmospheric pressure, and there is added to the calculated values of thespeed w of the pump a quantity w_(i) equal to the minimal speed to beapplied to the pump to obtain a non-zero vapor flowrate Q_(v), saidquantity W_(o) being measured between two dispensings of liquid.
 6. Amethod of recovering vapor emitted in a liquid dispensing installationduring the dispensing of a liquid into a tank, said installationcomprising:liquid dispensing means adapted to cause said liquid to flowwith a liquid flowrate Q_(L) between a storage tank and said tank; vaporrecovery means adapted to cause said vapor to flow with a vapor flowrateQ_(V) along a pipe between said tank and a recovery tank, said vaporflowrate Q_(V) being controlled by a parameter G (w ; R_(X))characteristic of said recovery means; said method including thefollowing steps:establishing an equation

    G=F(Q.sub.V, {p.sub.i })

relating the parameter G to the vapor flowrate Q_(V) and to parametersp_(i) characteristic of the recovery means and said pipe; determining aninitial value {p_(i) }_(o) of the parameters p_(i) ; and on eachdispensing k of liquid:measuring the liquid flowrate Q_(LK) anddetermining a value G_(K) of the parameter G to be imposed on therecovery means from the equation

    G.sub.k =F (Q.sub.Lk, {p.sub.i }.sub.k-1)

determining a new value {p_(i) }_(k) of the parameters p_(i) to be usedfor the next dispensing k+1 of liquid; wherein the recovery meanscomprises a pump, said parameter G is the rotation speed w of said pump;said pump having an internal leakage coefficient α with a non-zero valueand the pressures P' and P" at the inlet and the outlet of pump beingmaintained constant by means of pressure regulators, said equation

    w=F (Qv, {p.sub.i })

is given by:

    w=Q.sub.V P.sub.A /V.sub.G P'+a(P"-P')

where V_(G) is the geometrical cyclic volume of said pump and P_(A)atmospheric pressure, and wherein said parameters p_(i) comprise theparameters V_(G) and α, the constant parameter V_(G) is determined byinitial calibration of said pump, the value α_(k) of the parameter α oneach dispensing k being determined from the measured vapor flowrateQ_(V) of said pump using the equation:

    α.sub.k =(W.sub.k -Q.sub.vk P.sub.A /V.sub.G P')/(P"-P').


7. The method of claim 6, wherein said recovery tank has a pressuredifference of Δp_(o) relative to atmospheric pressure, and there isadded to the calculated values of the speed w of the pump a quantityw_(i) equal to the minimal speed to be applied to the pump to obtain anon-zero vapor flowrate Q_(v), said quantity W_(o) being measuredbetween two dispensings of liquid.
 8. A method of recovering vaporemitted in a liquid dispensing installation during the dispensing of aliquid into a tank, said installation comprising:liquid dispensing meansadapted to cause said liquid to flow with a liquid flowrate Q_(L)between a storage tank and said tank; vapor recovery means adapted tocause said vapor to flow with a vapor flowrate Q_(V) along a pipebetween said tank and a recovery tank, said vapor flowrate Q_(V) beingcontrolled by a parameter G (w; R_(X)) characteristic of said recoverymeans; said method including the following steps:establishing anequation

    G=F(Q.sub.V,{p.sub.i })

relating the parameter G to the vapor flowrate Q_(V) and to parametersp_(i) characteristic of the recovery means and said pipe; determining aninitial value {p_(i) }_(o) of the parameters p_(i) ; and on eachdispensing k of liquid:measuring the liquid flowrate Q_(LK) anddetermining a value G_(K) of the parameter G to be imposed on therecovery means from the equation

    G.sub.k =F (Q.sub.Lk, {p.sub.i }.sub.k-1)

determining a new value {p_(i) }_(k) of the parameters p_(i) to be usedfor the next dispensing k+1 of liquid; wherein the recovery meanscomprises a pump, said parameter G is the rotation speed w of said pump;and said recovery tank has a pressure difference ΔP_(o) relative toatmospheric pressure, and there is added to the calculated values of thespeed w of said pump a quantity w_(i) equal to the minimal speed to beapplied to the pump to obtain a non-zero vapor flowrate Q_(V), saidquantity w_(o) being measured between two dispensings of liquid.
 9. Themethod of claims 1, 2, 3, 4, 5, 6, 7, or 8, wherein one parameter p ofthe parameters p_(i) varies with the vapor flowrate Q_(V) such thataninitial table [P_(o) ^(j), Q_(v) ^(j) ] (j=1, . . . , N) is establishedlinking N values of the parameter p to N values of the vapor flowrateQ_(V) ; and on each dispensing k of liquid:in the equation

    G.sub.k =F(Q.sub.Lk, {P.sub.i }.sub.k-1)

a value p^(j) _(k-1) of the parameter p is used such that

    [p.sup.j.sub.k-1, Q.sup.j.sub.v =Q.sub.Lk ];

the vapor flowrate Q_(Vk) is measured and a corresponding value p_(k) ofthe parameter p is determined; a coefficient A_(k) is calculated suchthat

    A.sub.k =P.sub.k /p.sup.j'.sub.0 with [p.sup.j'.sub.0, Q.sup.j'.sub.V =.sub.Qvk ]; and

a new table[p^(j) _(k), Q^(j) _(V) ] is established with p^(j) _(k)=A_(k) p^(j) ₀ for any j.
 10. A method of recovering vapor emitted in aliquid dispensing installation during the dispensing of a liquid into atank, said installation comprising:liquid dispensing means adapted tocause said liquid to flow with a liquid flowrate Q_(L) between a storagetank and said tank; vapor recovery means adapted to cause said vapor toflow with a vapor flowrate Q_(V) along a pipe between said tank and arecovery tank, said vapor flowrate Q_(V) being controlled by a parameterG (w ; R_(X)) characteristic of said recovery means; said methodincluding the following steps:establishing an equation

    G=F(Q.sub.V,{p.sub.i })

relating the parameter G to the vapor flowrate Q_(V) and to parametersp_(i) characteristic of the recovery means and said pipe; determining aninitial value {p_(i) }_(o) of the parameters p_(i) ; and on eachdispensing k of liquid:measuring the liquid flowrate Q_(LK) anddetermining a value G_(K) of the parameter G to be imposed on therecovery means from the equation

    G.sub.k =F (Q.sub.Lk, {p.sub.i }.sub.k-1)

determining a new value {p_(i}) _(k) of the parameters p_(i) to be usedfor the next dispensing k+1 of liquid; wherein said recovery meanscomprises a pump and a solenoid valve, said parameter G is the hydraulicresistance R_(x) imposed by said solenoid valve, and the rotation speedw of the pump is constant; said solenoid valve being disposed downstreamof said pump, said pump having a non-zero internal leakage coefficientα, the equation

    R.sub.x =F(Q.sub.V, {p.sub.i } is given by:

    Rx=[W.sub.o -Q.sub.V /V.sub.G (1-R'Q.sup.n V/P.sub.A)-(αR)Q.sup.n V]/αQ.sup.2.sub.V

V_(G) being the geometrical cyclic volume of the pump, R' the hydraulicresistance of the pipe upstream of the pump, n a coefficient equal to7/4, P_(A) atmospheric pressure, R the hydraulic resistance of the pipe,equal to the sum of the upstream hydraulic resistance R' and thehydraulic resistance R" downstream of the pump, and wherein saidparameters p_(i) comprising V_(G), R', R and α, the constant parameterV_(G) is determined by initial calibration of the pump, the valuesR'_(k), R_(k) and α_(k) of the parameters R', R and α on each dispensingk being determined from the measured vapor flowrate Q_(V) and pressuresp' and P" at the inlet and at the outlet of the pump from the equations:

    R'.sub.k =(P.sub.A -P'.sub.k)Q.sup.n.sub.Vk

    R.sub.k =R'.sub.k +(P".sub.k -P.sub.A -R.sub.xk Q.sup.2.sub.Vk)/Q.sup.n.sub.Vk

    αk=[W.sub.o -Q.sub.Vk /V.sub.G (1-R'kQ.sup.n.sub.Vk /P.sub.A)]/(R.sub.k Q.sup.n.sub.Vk +R.sub.xk Q.sup.w.sub.Vk).


11. The method of claim 10, wherein one parameter p of the parametersp_(i) varies with the vapor flowrate Q_(V) such thatan initial table[P_(o) ^(j), Q_(v) ^(j) ] (j=1, . . . , N) is established linking Nvalues of the parameter p to N values of the vapor flowrate Q_(V) ; andon each dispensing k of liquid:in the equation

    G.sub.k =F(Q.sub.Lk, {P.sub.i }.sub.k-1)

a value p^(j) _(k-1) of the parameter p is used such that

    [p.sup.j.sub.k-1, Q.sup.j.sub.V =.sub.Qlk ];

the vapor flowrate Q_(Vk) is measured and a corresponding value p_(k) ofthe parameter p is determined; a coefficient A_(k) is calculated suchthat

    A.sub.k =P.sub.k /p.sup.j'.sub.0 with [p.sup.j'.sub.0, Q.sup.j'.sub.V =.sub.Qvk ]; and

a new tableis established with p^(j) _(k) =A_(k) p^(j) ₀ for any j.